This disclosure relates generally to a switching power supply and more particularly to detecting open connection faults of an auxiliary winding in a switching mode power supply.
Many electronic devices, including smart phones, tablets, and portable computers, employ power supplies providing controlled and regulated power output over wide operating conditions. These power supplies often include a power stage for delivering electrical power from a power source to a load across a transformer. A switch in the power stage electrically couples or decouples the load to the power source, and a switch controller coupled to the switch controls on-time and off-time of the switch. Regulation of the power output can be accomplished by, among other things, measuring the output current or output voltage and feeding that back to the primary-side switch controller. In order to improve cost performance and reduce size, many commercially available isolated power supplies employ primary-only feedback and control.
In power supplies using primary-side feedback and control, an auxiliary winding provides a feedback signal to the switch controller. By sensing primary side signals, the controller detects the secondary output and load conditions in order to control and regulate the output of the power supply. However, if the auxiliary winding is faulty or disconnected from the power supply, the switch controller does not receive an accurate feedback signal. Without an accurate feedback signal, the controller may not maintain operation of the power supply within overvoltage limits, resulting in possible damage to the power supply or a load driven by the power supply. It is therefore important to detect open connection faults of the auxiliary winding prior to using the auxiliary winding to provide feedback to the switch controller.